Pump

ABSTRACT

In a pump conveying a supercritical fluid or a liquid are provided stator slots and motor mold members which are charged between the stator slots, so as to have a stator can of a motor driving the pump from the outside thereof. Additionally, by providing a main shaft of a motor driving the pump and bearings supporting the main shaft with clearance-fitting and by tightening inner rings of the bearings to the main shaft in an axial direction, the bearings are fixed to the main shaft.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pump which conveys a supercriticalfluid or a liquid.

2. Description of the Prior Art

As one example of a pump which conveys a supercritical carbon dioxide(CO₂) fluid or a liquid carbon dioxide, there is a circulation pump forcleaning the semiconductors. Along with high integration of thesemiconductor devices in recent years, it is sought to have the wafersprocessed so as to be fine and minute in width. Therefore, against thepresent mainstream width of a wafer which is 0.18 μm, it is expectedthat the width thereof will be 0.10 μm or less. However, in thesemiconductor-cleaning method which uses a conventional liquid such asextra-pure water and the like, when the wafer is dried, there is a casewhere such a phenomenon occurs as a resist being formed to the wafer isdestroyed (“resist collapse”) by the capillary force which is caused bythe boundary tension between the gaseous body and the liquid.

In order to eliminate the above-mentioned disadvantage, is developed asemiconductor-cleaning equipment which uses a supercritical fluid,instead of the conventional liquid such as extra-pure water. Comparedwith a liquid, the supercritical fluid has a very high permeability andcan interpenetrate into any microscopic structure. In addition, becausethere exists no interface between the gaseous body and the liquid, ithas such a characteristic as the capillary force does not work at thedime of drying.

As the supercritical fluid, mainly carbon dioxide (CO₂) is used.Compared with other liquid vehicles, the carbon dioxide has a criticaldensity of 468 kg/m³ on relatively moderate conditions, namely, that thecritical temperature is 31.2° C. and the critical pressure is 7.38 Mpa.Furthermore, because the carbon dioxide is a gaseous body at a normaltemperature and at normal pressures, it is gasified by returning thetemperature and the pressure to be normal so that it is easy to separatean object to be cleaned from a contaminator. As a result, it will becomeunnecessary to dry the object to be cleaned after cleaning and the like,thereby making it possible to simplify the cleaning process and toreduce costs.

In such a semiconductor-cleaning equipment which uses a supercriticalCO₂ fluid as mentioned above, the supercritical CO₂ fluid is generallypressurized to be approximately 20 Mpa. Therefore, so-called“having-no-seals” canned motor pump type is used, which has highpressure-tightness and produces a small number of particles, as acirculation pump for cleaning of the wafers by circulating thesupercritical CO₂ fluid. Additionally, ball bearings are used forbearings, which are used in the fluid serving as a cleaning agent ofsemiconductors (supercritical CO₂ fluid).

The above-mentioned ball bearings receive the radial load and thrustload, which act on a rotor. Additionally, the preload is controlled by apreload spring which is installed to the bearing on the axial end side,being opposite to a bearing on the impeller side, which will bedescribed later, and thereby so-called revolution skidding (sideskidding) of a ball bearing is prevented. Moreover, rigidity (springconstant) in the radial direction of a ball bearing is controlled by thepreload of the bearing, thereby adjusting the natural vibrationfrequency of the rotor.

As for the rest, is disclosed a canned motor pump which has a filter forcapturing particles mounted in the fluid-introduction passageway. (Forexample, refer to the official bulletin of the Japanese PatentApplication Laid-Open No. H11-324971.) By this, solid particles beingincluded in the fluid are captured by the filter, so that the fluidcontaining no solid particles will be introduced into the inside of themotor. As a result, the fluid can flow smoothly in a narrow gap betweenthe bearings of the motor portion or between the cans and the like,thereby being able to perform cooling and lubrication without damagingthese members.

Or else, is disclosed a pump having a construction that integrates afluid machinery which is driven by a driving machine;flow-volume-control means which control the flow volume of the handledfluid flowing inside the fluid machinery; activating means which operatethe flow-volume-control means; and revolution-speed-control means whichcontrol the revolution speed of the driving machinery. (For example,refer to the official bulletin of the Japanese Patent ApplicationLaid-Open No. 2003-56469.) By this, it is possible to integrate thefluid machinery, the revolution-speed-control system and theflow-volume-control system as one package. As a result, it is possibleto simplify the installation work of the fluid machinery, therebyachieving labor-saving and natural-resources-saving.

However, in the future semiconductor-cleaning equipment, in order toenhance the cleaning ability of the wafers, it is necessary to increasethe conveying flow volume of the fluid serving as a cleaning agent.Therefore, a pump for conveying the fluid is required to have a highercapacity. On the other hand, in order to save the space of thesemiconductor-cleaning equipment, it is necessary to downsize the pumpfurther. Therefore, contradictory requirements for a pump for cleaningthe semiconductors, in other words, larger capacity and smaller size ofthe pump, must be satisfied.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a pump for asemiconductor-cleaning equipment which is in simple configurations, hasa large capacity but is small in size, and in addition, can assurereliability.

In order to achieve the above-mentioned object, according to the presentinvention, a pump which conveys a supercritical fluid or a liquid is soconstructed as stator slots and motor mold members which are chargedbetween the stator slots are installed, in order that the stator cans ofa motor driving the pump are supported from the outside thereof.

Moreover, a pump which conveys a supercritical fluid or a liquid is soconstructed as by providing clearance-fitting to a main shaft of a motordriving the pump and to bearings which support the main shaft and bytightening the inner rings of the bearings to the main shaft in theaxial direction, the bearings are fixed to the main shaft.

Additionally, a pump which conveys a supercritical fluid or a liquid isso constructed as the gap between a stator and a rotor is determined, inorder that the shaft system of a motor driving the pump is provided withdamping.

Furthermore, a pump which conveys a supercritical fluid or a liquid isso constructed as the distance between the bearings of the main shaft ofa motor is determined, in order that natural vibration frequency of themotor driving the pump deviates from the range of the revolution speed.

In addition, a pump which conveys a supercritical fluid or a liquid isso constructed as the thrust force which is applied to a rotor isadjusted by adjusting the cooling flow volume of a motor driving thepump as well as the configuration of a rotor.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing a construction ofa circulation pump for cleaning semiconductors in accordance with theembodiment of the present invention.

FIG. 2 is a longitudinal cross-sectional view of a stator having statorslots.

FIG. 3 is a longitudinal cross-sectional view of a necessary portion ofa bearing on the purging side and the vicinity thereof.

FIG. 4A and FIG. 4B depict a normal corrugated plate spring.

FIG. 5A and FIG. 5B depict the construction of a corrugated plate springto which end plates are added.

FIG. 6 is a graph showing the relation of the gap between the stator andthe rotor versus natural vibration frequency of the shaft system.

FIG. 7 is a longitudinal cross-sectional view showing a necessaryportion of a pump.

FIG. 8 is a graph showing an inward flow and the pressure distribution.

FIG. 9 is a graph showing an outward flow and the pressure distribution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, an embodiment of the present inventionwill be described hereinafter. The embodiment of the present inventionshows an example of a pump which conveys a supercritical CO₂ fluid, butis not limited to, and is applicable to a supercritical fluid, a liquidand the like in general. Additionally, concrete examples of thesupercritical fluid, the liquid and the like include CO₂, water,methanol and the like.

Embodiment

FIG. 1 is a longitudinal cross-sectional view showing a construction ofa circulation pump for cleaning semiconductors in accordance with theembodiment of the present invention. A circulation pump 1 has adischarge/suction-side casing 2, a purging-side casing 3 and an outercylinder 4 held by the discharge/suction-side casing 2 and thepurging-side casing 3. Outside the discharge/suction-side casing 2, isinstalled a manifold 5 which sucks and discharges the fluid.

Inside the outer cylinder 4 is installed a canned motor 6 which drivesthe circulation pump 1 and is provided with a stator 6 a outside thereofand a rotor 6 b being housed in the stator 6 a. The rotor 6 b isinstalled to a main shaft 7; and the main shaft 7 is supported on bothends thereof by an angular ball bearing 8 being installed to thedischarge/suction-side casing 2 and an angular ball bearing 9 beinginstalled to the purging-side casing 3 so as to rotate.

Between the discharge/suction-side casing 2 and the manifold 5 isinstalled an impeller 10, which is mounted onto one end of the mainshaft 7 and rotates simultaneously with the main shaft 7. The manifold 5has a suction port 5 a for the fluid mounted onto the extension linefrom one end of the main shaft 7; and has a spiral casing 5 b mountedaround the impeller 10. Additionally, a discharge port 5 c opens fromone portion of the periphery portion of the spiral casing/pathway 5 btoward the outer circumference surface of the manifold 5 in a radialdirection.

On the other hand, the purging-side casing 3 has a purging port 3 amounted onto the extension line from the other end of the main shaft 7,which discharges a part of the fluid being sucked. As for the rest, apreload spring 11 is held between the purging-side casing 3 and theangular ball bearing 9. This is a corrugated plate spring in a shape ofa ring being located in the vicinity of the other end of the main shaft7 and provides an axial preload to the angular ball bearing 9 as aconstant-pressure spring method.

In addition, the angular ball bearing 8 is referred as an impeller-sidebearing, while the angular ball bearing 9 is referred as ashaft-end-side bearing. The item 20 in the figure is a bolt whichconnects the discharge/suction-side casing 2 and the purging-side casing3; the item 21 is a bolt which connects the discharge/suction-sidecasing 2 and the manifold 5; and the item 22 is a socket for connectingto an electrical cable.

In a circulation pump 1 as described above, when the rotor 6 b of thecanned motor 6 and the main shaft 7 rotate, which makes the impeller 10rotate simultaneously, the fluid is sucked through the suction port 5 aas shown with an arrow A, introduced into the spiral casing/pathway 5 bby the centrifugal force of the impeller 10 and is discharged throughthe discharge port 5 c in the end as shown with an arrow B.Additionally, a part of the fluid being sucked through the suction port5 a passes between the angular ball bearings 8 and 9 and the main shaftstator in the canned motor 6, cooling them, and is discharged throughthe purging port 3 a as a purging flow, as shown with an arrow C.

Now, on the inner circumference surface of the above-mentioned stator 6a is installed a stator can 12 which is thin-walled and cylindrical. Onthe other hand, on the outer circumference surface of theabove-mentioned rotor 6 b is installed a rotor can 13 which isthin-walled and cylindrical. In the embodiment of the present invention,because a supercritical CO₂ fluid is conveyed by pressure feed, theinlet pressure of a pump becomes 20 MPa. However, because a canned motorpump has no seals, a pressure which is equivalent to the inlet pressureis provided to the motor portion, too.

Therefore, the motor portion is required to be so constructed as haspressure tightness. Furthermore, because strong acids such ashydrochloric acid, sulfuric acid, fluorinated acid, phosphoric acid andthe like are used as chemicals for cleaning the semi-conductors, themotor portion must be protected from these chemicals. In consequence,stainless steel (SUS 316L) having high corrosion resistance or HastelloyC-22 (R) is used for the stator can 12 and the rotor can 13.

However, when the wall thickness of the stator can is increased in orderto make the motor portion be constructed so as to have pressuretightness, a loss (eddy current loss) will be increased for an amount ofthe increase in wall thickness. Consequently, in order to restrain heatgeneration of the motor portion and besides increase the drivingefficiency, the stator can 12 cannot be made so thick. In other words, atrade-off designing is necessary, which takes account of the balancebetween enhancement of pressure-tight performance of the motor portionand reduction in loss. Therefore, in the embodiment of the presentinvention, the wall thickness of the stator can 12 is set to be 0.3 mm.

On the other hand, in order to obtain a certain level of large wallthickness of the stator can 12, it is necessary to enlarge the air gapof the motor portion. Therefore, in the embodiment of the presentinvention, the synchronous motor method is adopted, which can obtain arelatively larger air gap than the induction motor method. Additionally,as will be described hereinafter, stator slots, motor mold members(epoxy resin) and a reinforcement sleeve that are structures outside thestator can 12 are installed, serving as a pressure-tight constructionwhich supports the stator can 12.

-   -   FIG. 2 is a longitudinal cross-sectional view of a stator 6 a        having stator slots and depicts a cross section aa in FIG. 1. As        shown in this figure, a plurality number of stator core 6 abare        installed at equiangular intervals so as to protrude inward from        the inner circumference surface of a core 6 aa forming an        approximately cylindrical shape of the stator 6 a and form a        radial pattern. Between each of the stator core 6 ab is left        stator slots 6 acwhere a winding wire not being illustrated is        installed. Additionally, into the stator slots 6 ac is charged        epoxy resin, serving as a motor mold member, so as to cover the        winding wire. As described above, the stator can 12 being        thin-walled and cylindrical is installed on the inner        circumference surface of the stator 6 a, namely, on the end        surface of the stator core 6 ab , and is supported from the        outside by the stator core 6 ab and the motor mold member in the        stator slots 6 ac.    -   Now, in a stator 6 a, a portion having the above-mentioned        stator core 6 ab which is indicated with a dimension line “b” in        FIG. 1 can be utilized as a member providing strength. However,        because a portion having no stator slots which is indicated with        a dimension line “c” consists of only a winding wire 14 and a        motor mold member 15 which is installed so as to cover the        winding wire 14, a force being added to the stator can 12 from        the inside cannot be supported only by them, which causes the        stress being applied to the stator can 12 to be high.        Consequently, by installing a reinforcement sleeve 16 so as to        cover the inner circumference surface and the end surfaces of        the portion having no stator slots, the stator can 12 is        supported, thereby reducing the stress that is generated in the        stator can 12.

Chrome molybdenum steel SCM435 and the like are used for the material ofthe reinforcement sleeve 16. In addition, an O-ring slot 2 a isinstalled onto the outer circumference surface which shares a borderwith the stator can 12 of the discharge/suction-side casing 2 and anO-ring slot 3 b is installed onto the outer circumference surface whichshares a border with the stator can 12 of the purging-side casing 3,respectively; and seals are provided by the O-rings that are insertedinto these slots. As a result, it will not occur that the fluid flowsoutside of the stator can 12 and erodes the reinforcement sleeve 16.

Additionally, because the temperature of the fluid serving as asupercritical CO₂ fluid is as high as 60° C. and furthermore, becausethe calorific value inside the motor is large, the motor itself becomesas hot as 100° C. Meanwhile, because the above-described motor moldmember (epoxy resin) is considered as a structure member, epoxy resinmember having high glass-transition temperature (Tg) is used in order toprevent softening due to such high temperature. When the “Tg” valuelowers, it becomes easier for epoxy resin to be softened, thereby comingto play no role as a structure member. In addition, in order to let outthe heat from the motor to the outside, such epoxy resin member as hasgood heat conductance is selected. In this case, by adding, for example,alumina, silica, magnesia and the like to the epoxy resin member, heatconductance is improved.

Furthermore, because bearings are used in a supercritical CO₂ fluid (ora liquid CO₂) having low viscosity, lubrication provided by the fluidcannot be expected. Therefore, entire ceramics construction is adopted,which can extend the operating life even in such environments as havepoor lubricating property. Meanwhile, from the viewpoint of resistanceagainst chemicals, SUS 316L is adopted for the rotor (the main shaft).In consequence, the inner rings of the bearings are made of ceramics,while the rotor is made of SUS 316L, which makes the coefficients oflinear thermal expansion of both significantly different. To be moreprecise, the coefficient of linear thermal expansion of SUS is, forexample, 15.4×10⁻⁶(1/° C.); while the coefficient of linear thermalexpansion of ceramics is, for example, 3.4×10⁻⁶(1/° C.). Therefore,considering effects of an increase in temperature, both are subject toclearance-fitting.

FIG. 3 is a longitudinal cross-sectional view of a necessary portion ofa bearing on the purging side and the vicinity thereof. The degree ofthe above-mentioned clearance-fitting is set so as to obtain suchdimensional relation as the inner circumference surface of the angularball bearing 9 is attached firmly to the outer circumference surface ofthe main shaft 7 when the temperature, for example, increases to be ashigh as 150° C. Normally, because operation is performed in anenvironment having the temperature as high as 130° C. or less, it doesnot occur that the main shaft 7 expands excessively enough to destroythe angular ball bearing 9. Additionally, in order to prevent theangular ball bearing 9 from idle running due to execution of suchclearance-fitting, it is necessary to fix the angular ball bearing 9.Therefore, as shown in the figure, the angular ball bearing 9 istightened in the axial direction and fixed by using a bearing-retainingmechanism which is supplied by a bearing retainer 17 having anapproximately cylindrical shape.

To be more precise, by tightening the bearing retainer 17 to the mainshaft 7 in the axial direction with a bolt 18 which is threadablymounted into the center portion of the main shaft 7 and by catching aninner ring 9 a of the angular ball bearing 9 with the bearing retainer17 and the main shaft 7, the angular ball bearing 9 is fixed to the mainshaft 7. Same material, SUS 316L, that is used for the main shaft 7 isused for the bearing retainer 17; and for the bolt 18 is used a materialwhich has a smaller coefficient of linear thermal expansion than SUS316L. As a result of this, the bolt 18 will not be loosened even thoughthe temperature ascends. In addition, the same fixing method is takenfor the angular ball bearing 8 on the discharge/suction side, which isso constructed as has the inner ring of the angular ball bearing 8caught by the impeller 10 and the main shaft 7.

Moreover, as described above, such construction is adopted as thebearings and the motor are cooled while having a part of the flow fromthe inlet to the outlet run to the back surface of the impeller and passthrough a gap between the rotor and stator so as to flow out through thepurging port. In this case, by adjusting the inner construction of therotor, a design is made, so that the cooling flow volume is optimized.In other words, a trade-off design is performed, taking intoconsideration the cooling capacity and the efficiency of hydraulicpower.

Furthermore, it is necessary to add a preload in order to prevent thebearings from becoming deformed due to the centrifugal force and thetemperature and from skidding and to enhance the rigidity of thebearings. In the embodiment of the present invention, as shown in FIG.3, a load is provided to an outer ring 9 b of the angular ball bearing 9by using a preload spring 11 which is a corrugated plate spring. Inaddition, between the preload spring 11 and the purging-side casing 3 isinstalled a shim 19 which is shaped in a ring. By adjusting thethickness of this shim 19, the thrust force caused by the preload spring11 is adjusted. However, because the corrugated plate spring has anundulating construction having peaks and troughs and because the outerring 9 b of the angular ball bearing 9 slightly rotates, the peaks(portions which are subject to high pressure on the surface) are wornwhen a normal corrugated plate spring is used.

Such corrugated plate spring as described above is shown in FIG. 4A andFIG. 4B. FIG. 4A is a plan view thereof and FIG. 4B is a front viewthereof. These figures depict a corrugated plate spring which is shapedin a ring having three peaks. In the embodiment of the presentinvention, the preload spring 11 is so constructed as to have theconstruction of a corrugated plate spring to which end plates are addedas shown in FIG. 5A and FIG. 5B for purpose of decreasing such wear asmentioned above. FIG. 5A is a plan view thereof and FIG. 5B is a frontview thereof. This has both ends of a corrugated plate spring 11 aextended and has end plates 11 b in a shape of a flat washer formed onthe front-back both sides thereof. Because the flat end plates come toclosely contact with the outer ring of the bearing by this, the pressureon the surface which is in contact with the outer ring of the bearing isdecreased, thereby reducing the amount of wear.

Additionally, because a ball bearing is applied, damping which isprovided to the shaft system is small. Consequently, by making a gapbetween the rotor and the stator smaller, the damping of the shaftsystem is increased. In other words, as shown in the above-mentionedFIG. 3, by making the gap “G” between the stator can 12 and the rotorcan 13 smaller, the portion thereof is so constructed as to receiveeffects of the bearings. This will be described hereinafter as therelation between the gap and the vibration. First of all, because theobject of the present invention is a canned motor pump, the motor is incontact with the fluid. Additionally, the gap “G” between the stator andthe motor is narrow and the motor is cooled by having the fluid passthrough this gap.

As for the relation of the gap between the stator and the rotor with thenatural vibration frequency of the shaft system, a graph in FIG. 6 showsthe results of calculation by using an actual unit. In this figure, thehorizontal axis shows the revolution speed (rpm) and the longitudinalaxis shows the amplitude (μm). In this figure, the curve “a” shows acase where the gap “G” is 0.2 mm; the curve “β” shows a case where thegap “G” is 0.5 mm; and the curve “γ” shows a case where the gap “G” is0.6 mm, respectively; and the straight line “6” shows the revolutionspeed. The embodiment of the present invention exemplifies a case wherethe revolution speed is 30000 rpm.

As shown in this figure, when the gap of the motor is small (where “G”is 0.2 mm), added weight increases, which decreases the naturalvibration frequency of the shaft system. In this case, by providing thedamping to the shaft system by viscosity in the gap, it is possible tomake the value of the response to the vibration (Q factor) small.Additionally, when the gap of the motor is large (where “G” is 0.5 mm or0.6 mm), the added weight decreases, which increases the naturalvibration frequency of the shaft system. Here, when the gap is enlargedto a certain degree, there will be no difference in natural vibrationfrequency although the gap is increased furthermore. In this case,because the gap is large, so that no damping is provided, the value ofresponse to the vibration (Q factor) becomes large.

When a pump is operated at a high revolution speed, it is expected thatthe natural vibration frequency of the shaft system becomes smaller thanthe revolution speed. In this case, there is a concern that therevolution speed coincides with the natural vibration frequency whilethe pump is increasing the speed, which, eventually, makes operationbecome unstable. For a countermeasure to prevent such an unfavorableproblem as described above are considered a countermeasure to remove thecharacteristic value from the operating range and a countermeasure tolower the value of response (Q factor) in the characteristic value. Asdescribed above, when the gap is narrowed, the value of response can bedecreased; and when the gap is broadened, the value of response can beincreased. Therefore, in the embodiment of the present invention, byutilizing the narrow gap between the rotor and the stator, the optimumgap of the motor is determined from the operational revolution speed andthe characteristic value of the shaft system.

Additionally, by positioning the bearings inside the motor, the distancebetween the bearings and the length of the rotor are shortened. Byhaving the distance between the bearings shortened so as to increase thenatural vibration frequency in the bending mode and in addition, byhaving the weight of the rotor reduced so as to increase the naturalvibration frequency in all the modes, the natural vibration frequency isremoved from the range of revolution speed.

Furthermore, by adjusting the cooling flow volume and the configurationof the rotor, a thrust force being applied to the rotor system isreduced. Additionally, by using the outside diameter of the rotor forthe balance piston, the thrust force is adjusted. This will be describedhereinafter as a method of reducing the hydraulic load. To start with,because the object of the present invention is a canned motor pump, themotor is in contact with the fluid. Then, the pressure distribution isdifferent when the gap between the rotor and the stator is in the axialdirection from when the gap between the rotor and the stator is in theradial direction. When the gap between the rotor and the stator is inthe axial direction, static pressure decreases in accordance with thedirection of the flow. Meanwhile, when the gap between the rotor and thestator is in the radial direction, the static pressure increasestogether with an increase in radius, but the ratio of an increase instatic pressure differs, depending on the direction of the flow, the gapand the angle of evolution.

FIG. 7 is a longitudinal cross-sectional view showing a necessaryportion of a pump. Here, an axial force to the rotor being supplied bythe pressure of the fluid is obtained as a calculation of the thrustload. The alphabets “I” through “N” in the figure show major surfaceswhere the load is provided, and arrows show the distribution of loads oneach of the surfaces. When an inward flow is generated in the axial gap,the distribution of the static pressure changes as shown in the graph inFIG. 8. In this figure, the horizontal axis shows the radius, while thelongitudinal axis shows the static pressure. Additionally, the curve “α”shows a case where the flow volume is small; the curve “β” shows a casewhere the flow volume is medium; and the curve “γ” shows a case wherethe flow volume is large, respectively.

As shown in FIG. 8, pressure difference between the inlet and the outletbecomes large concurrently with an increase in flow volume (indicatedwith an arrow). Additionally, when the revolution speed of the fluidincreases, the pressure difference is increased. When it is desired tomake the revolution speed of the fluid larger, it can be achieved by,for example, installing blades in a shape of a plate to the rotor. Onthe contrary, when it is desired to make the revolution speed smaller,it can be achieved by installing the blades of the same kind to thestator.

Moreover, when an outward flow occurs in the axial gap, the distributionof the static pressure changes as shown in the graph in FIG. 9. In thisfigure, the horizontal axis shows the radius, while the longitudinalaxis shows the static pressure. In addition, the curve “α” shows a casewhere the flow volume is small; the curve “β” shows a case where theflow volume is medium; and the curve “γ” shows a case where the flowvolume is large, respectively.

As shown in FIG. 9, the pressure difference between the inlet and theoutlet becomes small concurrently with an increase in the flow volume(indicated with an arrow). Additionally, when the revolution speed ofthe fluid increases, the pressure difference is increased. When it isdesired to make the revolution speed of the fluid larger, it can beachieved by, for example, installing blades in a shape of a plate to therotor. On the contrary, when it is desired to make the revolution speedsmaller, it can be achieved by installing the blades of the same kind tothe stator. Furthermore, as shown in each of the figures, when the flowvolume is the same, comparison of an inward flow with an outward flowshows that the inward flow has a larger difference in static pressurebetween the inlet and the outlet.

Next, a method of adjustment of the thrust will be described. When thethrust load being applied to the rotor is provided in the direction ofthe impeller, the revolution speed of the fluid is increased byinstalling the blades to the surfaces “M” and “N” of the rotor in FIG.7, thereby increasing the reduction in pressure between the inlet andthe outlet. Moreover, by making an annular gap of the portion “E” small,so as to cause a pressure loss in the portion “E,” the thrust load isdecreased. Additionally, by enlarging the outside diameter “D” of therotor, so as to increase the region of load on the surfaces “L” and “M,”the load in the direction of the shaft ends is increased. This isattributed to a larger pressure difference between the inlet and theoutlet of the inward flow than that of the outward flow, when the flowvolume is the same.

Additionally, when the thrust load being applied to the rotor isprovided in the direction of the shaft ends, the revolution speed of thefluid is decreased by installing the blades to the static surfacesagainst the surfaces “M” and “N” in FIG. 7, thereby decreasing thereduction in pressure between the inlet and the outlet. Furthermore, byenlarging the annular gap of the portion “E,” the pressure lossgenerating in the portion “E” is decreased, thereby reducing the thrustload. In addition, by making the outside diameter “D” of the rotorsmall, so as to decrease the region of load on the surfaces “L” and “M,”thereby reducing the load in the direction of the shaft ends. Bychanging the construction as described above, the hydraulic thrust loadis made zero (0).

1. A pump conveying a supercritical fluid or a liquid, comprising: asuction-side casing forming a body of the pump and having an inletthrough which the supercritical fluid or liquid is supplied into thesuction-side casing and an outlet through which the supercritical fluidor liquid having a pressure thereof raised is discharged out of thesuction-side casing; an impeller provided inside the suction-side casingand raising the pressure of the supercritical fluid or liquid presentbetween the inlet and outlet of the suction-side casing; a purging-sidecasing having a purging port through which part of the pumped liquidobtained by sucking in the supercritical fluid or liquid is discharged;an outer cylinder held between the suction-side casing and thepurging-side casing; a main shaft provided in a central part of theouter cylinder and connected to the impeller to transmit a rotatingforce thereto; a first ball bearing supporting the main shaft in thesuction-side casing; a second ball bearing supporting the main shaft inthe purging-side casing; a stator arranged inside the outer cylinder andhaving a winding arranged on a stator core formed as projections formedon an inner circumferential surface of a cylindrical core; a rotorarranged inside the stator and arranged on an outer circumferentialsurface of the main shaft; a stator can provided inside the stator toprevent the part of the pumped liquid from entering the stator; a rotorcan provided outside the rotor to prevent the part of the pumped liquidfrom entering the rotor; a motor mold member filling the inside andoutside of the stator, outside of the stator can; a reinforcement sleeveprovided to cover an inner circumferential surface and end surfaces ofthe motor mold member located where the stator does not exist outsidethe stator can; and an O-ring provided on a surface at which thesuction-side and purging-side casings make contact with the stator can.2. A pump as claimed in claim 1, wherein the first ball bearing is fixedas a result of an inner ring thereof being held between the impeller andthe main shaft, and the second ball bearing is fixed as a result of aninner ring thereof being held between a bearing retainer and the mainshaft, the bearing retainer being fastened with a bolt screwed into acenter portion of the main shaft.
 3. A pump as claimed in claim 2,further comprising: preload spring applying a preload to the second ballbearing, wherein the preload spring is a single member having,integrally formed, a corrugated plate spring and end plates formed byextending both ends of the corrugated plate spring to have a shape of aflat washer.
 4. A pump as claimed in claim 1, wherein a gap between astator and a rotor is determined, so as to provide a shaft system of amotor driving said pump with damping.
 5. A pump as claimed in claim 1,wherein a distance between bearings of a main shaft of said motor isdetermined to have natural vibration frequency of a motor driving saidpump deviate from a region of revolution.
 6. A pump as claimed in claim1, wherein, by adjusting a cooling flow volume of a motor driving saidpump and a configuration of a rotor, thrust force being applied to arotor is adjusted.
 7. A pump as claimed in claim 1, wherein thesupercritical fluid or liquid conveyed by the pump contains an acidicfluid.
 8. A pump as claimed in claim 1, wherein the reinforcement sleeveis formed of chromium molybdenum steel.
 9. A pump as claimed in claim 1,wherein the stator can is formed of an acid-resistant material.
 10. Apump conveying a supercritical fluid or a liquid, comprising: asuction-side casing forming a body of the pump and having an inletthrough which the supercritical fluid or liquid is supplied into thesuction-side casing and an outlet through which the supercritical fluidor liquid having a pressure thereof raised is discharged out of thesuction-side casing; an impeller provided inside the suction-side casingand raising the pressure of the supercritical fluid or liquid presentbetween the inlet and outlet of the suction-side casing; a purging-sidecasing having a purging port through which part of the pumped liquidobtained by sucking in the supercritical fluid or liquid is discharged;an outer cylinder held between the suction-side casing and thepurging-side casing; a main shaft provided in a central part of theouter cylinder and connected to the impeller to transmit a rotatingforce thereto; a first ball bearing supporting the main shaft in thesuction-side casing; a second ball bearing supporting the main shaft inthe purging-side casing; a stator arranged inside the outer cylinder andhaving a winding arranged on a stator core formed as projections formedon an inner circumferential surface of a cylindrical core; a rotorarranged inside the stator and arranged on an outer circumferentialsurface of the main shaft; wherein, the first ball bearing is fixed as aresult of an inner ring thereof held between the impeller and the mainshaft, and the second ball bearing is fixed as a result of an inner ringthereof being held between a bearing retainer and the main shaft, thebearing retainer being fastened with a bolt screwed into a centerportion of the main shaft.
 11. A pump as claimed in claim 10, furthercomprising: a preloaded spring applying a preload to the second ballbearing. wherein the preload spring is a single member having,integrally formed, a corrugated plate spring and end plates formed byextending both ends of the corrugated plate spring to have a shape of aflat washer.